In order to improve efficiency, control and performance of internal combustion engines, there has been a trend in the industry to adopt hydraulically-actuated electronically controlled systems in place of the cam driven systems long known in the art. For instance, Caterpillar, Inc. of Peoria, Ill. has observed considerable success by substituting its hydraulically-actuated electronically controlled fuel injection systems into diesel engines in place of the cam driven fuel injectors of the prior art. These hydraulically-actuated fuel injectors typically employ engine lubricating oil that is raised to a relatively high pressure as the hydraulic actuating medium. In many instances, a plurality of hydraulically-actuated fuel injectors are connected to single high pressure rail containing pressurized lubricating oil. In order for the hydraulically-actuated system to perform as expected, there must typically be some means provided for controlling the magnitude of fluid pressure in the high pressure common rail.
In the case of Caterpillar, Inc. hydraulically-actuated fuel injection systems, the high pressure common rail is maintained in a pressurized state by a swash plate type pump that is coupled directly to the engine. The fluid demands on the common rail increase with engine speed and load since the fuel injectors are required to inject a larger amount of fuel at higher engine operating conditions. By correctly sizing the high pressure pump and coupling the same directly to the engine, the output of the pump can be made to satisfy the demand of the fuel injectors over the operating range of the engine. However, in order to insure that there is adequate pressure at all times, the high pressure pump is generally sized to produce more high pressure fluid than is required across the engine's operating range. Since the high pressure pump is constantly producing more high pressure fluid than the fuel injectors use in their normal operation, an electronically controlled rail pressure control valve continuously drains an amount of pressurized fluid from the rail to maintain the common rail at a desired pressure.
Those skilled in the art will appreciate that draining pressurized fluid from the common rail without obtaining useful work, results in a waste of energy and a decrease in the overall efficiency and performance of the engine. The use of an electronically controlled rail pressure control valve is also less than desirable in that it requires a separate actuator and control logic. Furthermore, since the prior art pressure regulation system requires an oversized pump, there also remains room for improvement in having an ability to more closely match the output of the high pressure pump to the demands of the hydraulically-actuated fuel injection system.
The present invention is directed to improving upon hydraulically-actuated systems of the prior art.